This is a continuing volunteer donor protocol that is sub-part of the Baltimore Longitudinal Study of Aging (BLSA) with Dr. Eric H. Westin as the current Principal Investigator. In this protocol, volunteers are recruited to undergo a two hour cytapheresis procedure for collection of large quantities of human ciculating white blood cell components (lymphocytes or monocytes) from single donors for banking and direct use by a variety of National Institute on Aging laboratory investigators. Pheresis packs are supplied to the NIA Clinical Core Laboratory for banking. Individual qualified investigators receive portions of anonymous packs from the Clinical Core Laboratory for use in genetic studies as DNA and in studies of lymphocyte and monocyte function and studies of immune function in the aging process. Based on extensive modified American Bloodbank Association questionaires, laboratory screening including assessment of complete blood counts, urinalysis, liver and renal function as well as virologic screening including HIV and Hepatitis testing, the possibility of influence of extraneous infections on laboratory studies is minimized. In the course of the last year, a total of 465 BLSA participants underwent initial screening. Of these, 67 underwent full donor screening with 30 procedures performed. Pheresis packs were distributed to the Clinical Core Laboratory. Based on trends in the current year, it is expected that an increased number of participants will participate in this study within the BLSA in the next year.